DOYLESTOWN, Pa. -- Over beers at a small pub here an hour north of Philadelphia, a handful of Tea Party activists were blunt when asked whether they thought Rick Santorum might lose the Pennsylvania presidential primary in less than three weeks.

"I don't think he's going to win his own state," said Ana Puig, a 40-year old mother of four who helps lead a prominent grassroots group.

If Puig is right, it’s lights out for the former U.S. senator from this state, whether he keeps his campaign going or not into May. After Romney’s wins in Wisconsin, Maryland and Washington, D.C., Santorum’s candidacy is hanging by a thread.

Puig, a state coordinator for FreedomWorks, a Washington, D.C.-based group, said Santorum was incapable of beating President Barack Obama in the fall.

"He pushes the social conservatism way too much. It is a blue state,” she said of Pennsylvania. “What brings us together is fiscal responsibility and I don't think he's got the greatest fiscal record as far as when he was down in Washington, D.C.”

Richard Tems, who owns a small manufacturing company in nearby Jamison and had just attended a monthly activist bull session on the second floor of Bobby Simone’s bar with Puig and 20 others, agreed.

Tems said Santorum "still has a good base, he still has a lot of people." But his loss to Mitt Romney in Wisconsin on Tuesday night "might be enough for him to lose" in Pennsylvania, Tems said.

"You can only run an underground campaign for so long and I think he's reached that point," Tems said.

SANTORUM'S 'CLEAR LEAD'

It's not clear whether Puig and Tems speak for the majority of the Pennsylvania's conservative grassroots. Jennifer Stefano, the state coordinator for Americans for Prosperity, another D.C.-based conservative group, said that “Santorum is very, very popular among our activist base.”

Polling shows Santorum ahead of Romney, the former Massachusetts governor. But his lead has shrunk from double-digits in early March to about 7 percentage points in the Real Clear Politics average. And as the attention of the state and the country shifted here immediately after results from Wisconsin, Maryland and Washington, D.C., were announced Tuesday night, the expectation was that Romney's campaign and a super PAC supporting him will go for the kill.

"Rick has a clear lead across the state right now, but there's one thing that's going to change the dynamic in Pennsylvania, and that's tens of millions of dollars of advertising for Romney, which will no doubt close the race," said Ray Zaborney, a political consultant and lobbyist based in Harrisburg.

Restore Our Future, the pro-Romney super PAC, has already been running a small amount of TV advertising, and state Sen. Jake Corman, a Republican from central Pennsylvania who has endorsed Santorum, told HuffPost he has already received eight automated robocalls to his home from the Romney campaign.

"And we've still got three weeks until the election," said Corman.

Romney himself will travel to Philadelphia's western suburbs on Wednesday afternoon for a rally in Broomall, a sign that he intends to go for Santorum’s jugular.

For the Romney high command in Boston, talk of a victory over Santorum here is the equivalent of dangling a 48-ounce porterhouse steak in front of a starved Doberman pinscher.

It would finish off a three-punch combination that started with Romney's win in Illinois on March 20 and continued Tuesday with the victory in Wisconsin, setting up the contest in the Keystone State on April 24.

Pennsylvania's primary will be held the same day as contests in four other states -- all likely to go into Romney's win column: New York, Connecticut, Rhode Island and Delaware.

Gail Gitcho, a spokeswoman for the Romney campaign, set expectations low when asked about Romney's chances of winning Pennsylvania.

"We will campaign there and hope to earn as many delegates as we can, but we expect Santorum to win his home state, just like Romney won Massachusetts and Newt [Gingrich] won Georgia," Gitcho said in an e-mail.

But Austin Barbour, a Mississippi lobbyist who is also a national finance chairman for Romney, began to put pressure on Santorum to think about the ramifications for his political and personal legacy if he were to lose a big race in Pennsylvania again, six years after losing his Senate seat by 18 percentage points to Bob Casey, a Democrat.

“There's no question he doesn't want to end this race with a loss in his home state. The guy has run a hard-fought campaign,” Barbour said of Santorum in an interview.

Barbour didn’t predict a win for Romney in the state, but sought to sow doubt about whether Santorum should continue if it looks, two weeks or so from now, like the candidate might lose on April 24.

“He's the favorite on paper and he's the favorite in polls, but it's not a slam-dunk,” Barbour said.

'WE'VE KNOWN HIM FOR 16 YEARS'

There is good reason, however, for the Romney campaign to avoid feeding expectations of a knockout in Pennsylvania.

Santorum's political standing was greatly diminished by his embarrassing Senate defeat in 2006. But it's still not clear how much damage Santorum suffered among Republican voters.

"Republican primary voters have voted for Rick three different times," Zaborney said, referring to his Senate campaigns in 1994, 2000 and 2006. "These are the same voters who made up Rick's base in the 2006 race when he lost. All these voters just voted for him at his lowest political moment."

Corman, whose family has a longstanding and unique relationship with Santorum (Santorum worked for Corman's father in the state legislature and Corman's mother ran Santorum's grassroots operation for years) said the candidate is inoculated against political attacks in his home state.

"I don’t think [Romney will] be able to drive the senator's negatives up where we've known him for 16 years," Corman said. "Everyone knows who Rick Santorum is. Even in the election that he lost, he did very well among Republicans."

But a good number of the Republican establishment in the state, which of course was with Santorum in that general election showdown with Casey six years ago, is with Romney now.

"There are many people like myself who have supported Rick Santorum every time he has run who feel sincerely that Rick Santorum is not in a position to be competitive in Pennsylvania [in the general election this fall], and we think that's clearly going to be a liability nationally as well," former Rep. Phil English, (R-Pa.) said in an interview.

"Rick Santorum has to win a very large majority of those delegates to be viable, whatever happens with the beauty contest," English said. "The odds right now favor him splitting it 50-50 with Romney and very possibly coming in with fewer delegates than Romney."

"If that's the case, then I think it finishes him politically, or at least it should."

PENNSYLVANIA'S UNUSUAL DELEGATES

Most of the state's 72 delegates will be elected to the national convention on April 24 by voters themselves, which is unusual. Most states have conventions, where voters elect delegates to county conventions, who then vote at a later date to elect delegates to the state convention, and it's only at the state convention that delegates to the national convention are chosen.

In Pennsylvania, however, the delegates who get the most votes from each congressional district go straight to Tampa. They are not required to state which candidate they support and their allegiance is not indicated on the ballot. So it's crucial for presidential campaigns to have as many supporters running for delegate spots as possible.

Zaborney said that Santorum "doesn't have as many delegates filed" as Romney, but has many supporters who are public officials with names that are well known to most voters.

"A lot of the delegates who have filed are state senators and elected officials in some of the bigger counties and congressional districts, so I give them pretty good odds of winning," Zaborney said.

And not everyone in the state and local GOP machinery is enthused about Romney, said one source in the state legislature close to the Republican leadership, who asked not to be identified in order to speak more frankly about the views of senior political figures.

"I don't think there's love for Romney, listening to the leaders around the state," the statehouse insider said. Santorum "clearly offers a desirable but probably not an electable alternative. Everybody's watching him with interest and shock that he's doing so well."

Even if Santorum were to lose Pennsylvania, one veteran Republican operative said she thinks he will stay in the race because there are Southern state primaries that he may win in May.

"In May, Santorum is likely to win a number of states: Texas, West Virginia, Arkansas, North Carolina, Kentucky," Juleanna Glover, a former White House official under President George W. Bush, said on MSNBC. "So I just don't see him getting out whether or not he wins or loses Pennsylvania."

In an e-mail, Glover defended her point, saying a loss in Pennsylvania would not erase Santorum's support among his core constituency.

"Southern evangelicals will never abandon Rick Santorum as long as he's in race. Pennsylvania is a foreign country to them. It won't matter," Globver said.

That diehard support is not enough to give Santorum a realistic shot at the nomination. But it is enough to drag the primary all the way to June 5, when California and New Jersey will award 172 delegates and 50 delegates, respectively, in contests sure to favor Romney.

That, ultimately, is likely to be the final blow to Santorum's upstart candidacy.